1. Field of the Invention
The invention relates to a temperature limiter for a glass-ceramic cooking unit, and in particular to one having a substantially rod-shaped temperature sensor which has an outer tube containing an inner rod with a different coefficient of expansion. The rod actuates a signal switch disposed in a base to indicate the heating state of the glass-ceramic cooking surface and actuates via a pivotable lever a circuit breaker also disposed in the base for switching the heating system of the glass-ceramic cooking unit off at a limiting temperature lying just below the permissible temperature of the glass-ceramic cooking surface.
2. Prior Art
A temperature limiter of the general kind specified is known (German Offenlegungsschrift No. 28 39 161 dated Mar. 20, 1980). In that prior art apparatus the temperature sensor is mounted to be pivoted in relation to the base via ball bearings. The signal switch is actuated by the same lever which also actuates the circuit breaker. The temperature sensor is engaged with a point on the lever lying between the two switches, so that any increase in the travel of the temperature sensor is used for actuating the signal switch. With this prior art temperature switch adjustment can be performed only when the temperature limiter is attached to the heating element of the glass-ceramic cooking unit. The temperature sensor is rigidly fixed on the sheet metal plate, while the base can be aligned to some extent due to the pivotable construction. Only then can adjustment be performed. It has been found that during the operation of the apparatus the adjustment may alter, due to the influences of ageing and also mechanical displacements.
An electric cooking apparatus is also known which has a temperature limiter expansion member acting on two switch contacts, one of which is used for the indication of a signal device, the other being used for switching off the heating system (German Patent No. 27 48 109 published May 3, 1979). To this end a wire disposed in the tube is clamped to a resilient strip whose free, lever-forming end has an insulating member which actuates the two contacts.